U.S. patent application number 10/594145 was filed with the patent office on 2007-09-20 for gas discharge display panel.
Invention is credited to Jun Hashimoto, Masatoshi Kitagawa, Mikihiko Nishitani, Masaharu Terauchi, Shinichi Yamamoto.
Application Number | 20070216302 10/594145 |
Document ID | / |
Family ID | 35125341 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070216302 |
Kind Code |
A1 |
Hashimoto; Jun ; et
al. |
September 20, 2007 |
Gas Discharge Display Panel
Abstract
Provided is a gas discharge display panel that exhibits a
favorable display performance by maintaining a wall charge
retaining power, controlling discharge delay within a range
adequate for optimal image display, and reducing the discharge
starting voltage at comparatively low cost. Also provided is a PDP
that exhibits more reliability with enhanced display quality by
further improving the secondary electron emission factor .gamma.
compared to conventional cases and lowering the discharge starting
voltage to widen the driving margin. In addition, provided is a
manufacturing method of a gas discharge display panel, by which the
manufacturing cost lowers by reduction of the exhaustion time in
the sealing exhaustion process, and by which the driving circuit
cost is reduced. In the present invention, the protective layer
contains, with respect to a MgO content of the protective layer, Si
in a range of 20 mass ppm to 5000 mass ppm inclusive and H in a
range of 300 mass ppm to 10000 mass ppm inclusive.
Inventors: |
Hashimoto; Jun; (Osaka,
JP) ; Kitagawa; Masatoshi; (Osaka, JP) ;
Nishitani; Mikihiko; (Nara, JP) ; Terauchi;
Masaharu; (Nara, JP) ; Yamamoto; Shinichi;
(Osaka, JP) |
Correspondence
Address: |
SNELL & WILMER L.L.P. (Matsushita)
600 ANTON BOULEVARD
SUITE 1400
COSTA MESA
CA
92626
US
|
Family ID: |
35125341 |
Appl. No.: |
10/594145 |
Filed: |
April 7, 2005 |
PCT Filed: |
April 7, 2005 |
PCT NO: |
PCT/JP05/06884 |
371 Date: |
September 26, 2006 |
Current U.S.
Class: |
313/567 |
Current CPC
Class: |
H01J 11/12 20130101;
H01J 11/40 20130101 |
Class at
Publication: |
313/567 |
International
Class: |
H01J 11/02 20060101
H01J011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 8, 2004 |
JP |
2004-113789 |
Jun 2, 2004 |
JP |
2004-164952 |
Mar 9, 2005 |
JP |
2005-065504 |
Claims
1. A gas discharge display panel comprising a substrate, a
dielectric layer, and a protective layer, the dielectric layer and
the protective layer being formed in the stated order on a surface
of the substrate, wherein the protective layer contains H in a
range of 300 mass ppm to 10000 mass ppm inclusive with respect to a
MgO content of the protective layer.
2. The gas discharge display panel of claim 1, wherein the H
content of the protective layer is in a range of less than 1500
mass ppm with respect to the MgO content.
3. The gas discharge display panel of claim 1, wherein the
protective layer further contains Si in a range of 20 mass ppm to
5000 mass ppm inclusive with respect to the MgO content.
4. The gas discharge display panel of claim 1, wherein the
protective layer further contains Ge in a range of 10 mass ppm or
above and below 500 mass ppm with respect to the MgO content.
5. A gas discharge display panel comprising a substrate, a
dielectric layer, and a protective layer, the dielectric layer and
the protective layer being formed in the stated order on a surface
of the substrate, wherein when the protective layer is subjected to
a cathodoluminescence spectroscopy, a relative are a intensity of a
first intensity with respect to a second intensity for a light
emission peak are a is in a range of 0.6 to 1.5 inclusive, where
the first intensity is a light emission peak intensity generated in
a wavelength range of 720 nm or above and below 770 nm and the
second intensity is a light emission peak intensity generated in a
wavelength range of 300 nm or above and below 450 nm.
6. The gas discharge display panel of claim 5, wherein the
protective layer contains H in addition to MgO.
7. The gas discharge display panel of claim 5, wherein the
protective layer contains H and Si in addition to MgO, where the Si
content is in a range of 20 mass ppm to 5000 mass ppm inclusive
with respect to the MgO content.
8. A gas discharge display panel comprising a substrate, a
dielectric layer, and a protective layer, the dielectric layer and
the protective layer being formed in the stated order on a surface
of the substrate, wherein when the protective layer is subjected to
a cathodoluminescence spectroscopy, a relative are a intensity of a
second intensity with respect to a third intensity for a light
emission peak are a is in a range of 0.9 or above, where the second
intensity is a light emission peak intensity generated in a
wavelength range of 450 nm or above and below 600 nm and the third
intensity is a light emission peak intensity generated in a
wavelength range of 300 nm or above and below 450 nm.
9. The gas discharge display panel of claim 8, wherein the
protective layer contains H in addition to MgO.
10. The gas discharge display panel of claim 8, wherein the
protective layer contains H and Ge in addition MgO, where the Ge
content is in a range of 10 mass ppm to 300 mass ppm inclusive with
respect to the MgO content.
11. The gas discharge display panel of claim 7, wherein the
protective layer contains Ge in a range of 10 mass ppm or above and
below 300 mass ppm with respect to the MgO content.
Description
TECHNICAL FIELD
[0001] The present invention relates to a gas discharge display
panel such as a plasma display panel. The present invention
particularly relates to a technology for improving a protective
layer.
BACKGROUND ART
[0002] G as discharge display panels, represented by a plasma
display panel (herein after simply "PDP"), are display apparatuses
that display images by light emission performed by exciting
phosphors by means of ultraviolet light generated by gas discharge.
According to the discharge forming method, PDPs are divided into
two types of alternating current (AC) type and direct current (DC)
type, where the AC type is most common because of superiority over
the DC type in terms of brightness, light emission efficiency, and
lifetime.
[0003] As is disclosed in Patent reference 1 for example, an
AC-type PDP has the following structure. Two thin glass panels
respectively provided with a plurality of electrodes (either
display electrodes or address electrodes) and a dielectric layer
are placed to oppose each other with a plurality of barrier ribs
therebetween. A phosphor layer is provided so that phosphors are
positioned between adjacent barrier ribs, thereby forming a
plurality of discharge cells in matrix formation. The space between
the two glass panels is filled with discharge gas. Furthermore, a
protective layer (film) is provided on a surface of the dielectric
layer covering the display electrodes.
[0004] While driving a PDP, power is supplied as necessary to the
plurality of electrodes in a plurality of subfields that include an
initialization period, an address period, a sustain period, and so
on, according to a field time-sharing grayscale display method,
thereby causing phosphor light emission by means of ultraviolet
light generated by obtaining discharge in the discharge gas.
[0005] Here, a material for the protective layer provided for the
front glass panel is required to generate discharge at a low
discharge starting voltage while protecting the dielectric layer
from ion bombardment incident to discharge at the same time. For
this purpose, a material mainly made of magnesium oxide (MgO) is
widely used for the protective layer of PDPs, as is disclosed in
Patent reference 2, for MgO has an excellent sputtering resistant
characteristic and a large secondary electron emission factor.
[0006] The conventional protective layer has the following
problems. The first problem is that conventional protective layers
are susceptible to "discharge delay". The discharge delay is a
phenomenon caused in the address period, which specifically
corresponds to a time lag from application of a pulse for address
discharge to when actual discharge to take place. If the discharge
delay is large, the possibility of preventing address discharge
from occurring even at the end of the address pulse application
becomes high, with which writing defect is likely caused. This
phenomenon is more frequent in high-speed driving. The problem of
discharge delay is a problem to be solved for improving image
display performance of PDPs.
[0007] So as to counter this problem of discharge delay, a
technology was already proposed to reduce the time lag by adding a
predetermined amount of Si to MgO, as is disclosed in Patent
references 3 and 7, for example. Furthermore, Patent reference 4
discloses a technology of attempting to reduce the time lag by
adding a predetermined amount of H to the protective layer. Still
further, Patent reference 5 discloses a technology of attempting to
reduce the time lag by adding Ge.
[0008] The second problem is a characteristic change of the
protective layer.
[0009] To be more specific, a surface of the protective layer is
exposed in the discharge space. However the metal oxide film such
as the MgO film has a characteristic that absorbs gas such as water
(H.sub.2O) and carbon dioxide (CO.sub.2), which then would easily
generate hydroxide compounds and carbonate compounds. In a process
performed in the air from among the PDP manufacturing processes, a
protective layer made of MgO tends to be contaminated by absorption
of oil impurity, CO.sub.2, and H.sub.2O. When the absorption gas is
absorbed by the surface of the MgO, the characteristic of the
protective layer changes, thereby decreasing the secondary electron
emission efficiency. As a result, the discharge starting voltage is
raised, narrowing the driving margin of a PDP.
[0010] Furthermore, according to the level of absorption of gas for
example by the protective layer, the discharge starting voltage is
varied for each discharge cell. This would lead to a problem of
display defect called "black noise" which specifically is a
phenomenon in which accurate display of intended cells is
impaired.
[0011] Therefore conventionally, the protective layer has a
two-layer structure, as disclosed by Patent reference 6 for
example, to improve quality and enhance stability. The disclosure
specifically discloses a two-layer structure in which a second
protection film is provided on a first protection film, where the
first protection film has a comparatively excellent discharge
characteristic and is (111) oriented, and the second protection
film has such a film characteristic that hardly absorbs gas and has
small moisture absorption, thereby attempting to prevent absorption
of water molecules and impurity gas such as CO.sub.2.
Patent reference 1: Japanese Patent Publication No. H9-92133
Patent reference 2: Japanese Patent Publication No. H9-295894
Patent reference 3: Japanese Patent Publication No. H10-334809
Patent reference 4: Japanese Patent Publication No. 2002-33053
Patent reference 5: Japanese Patent Publication No. 2004-31264
Patent reference 6: Japanese Patent Publication No. 2003-22755
Patent reference 7: Japanese Patent Publication No. 2004-134407
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0012] However, the first problem can hardly be said to have been
resolved at the current state.
[0013] Concretely, it is confirmed that the technology of Patent
reference 3, although restraining generation of non-lighted are a
to some extent, produces a new problem of accentuating variations
in discharge delay according to cells.
[0014] In addition, the inventors of the present invention have
confirmed that the technology of Patent reference 4, although
restraining discharge delay by addition of H to MgO, reduces
retaining power of the wall charge, which makes it difficult to
generate optimal discharge for image display.
[0015] Furthermore, measurement tests have revealed that the
technology of Patent reference 5 has insufficient effect of
restraining discharge delay as well as raising the discharge
starting voltage. Accordingly, the technology of Patent reference 5
can hardly be said to produce a sufficient effect in obtaining
excellent display qualities.
[0016] So as to treat the mentioned problems regarding protective
layer, a possible method is to increase the operating voltage of a
PDP while adopting a high resistance transistor and a driver IC as
a driving circuit and an integrated circuit. However this method is
not desirable in that it incurs high power consumption and high
cost for PDPs.
[0017] Furthermore, the following problems are unsolved regarding
the stated second problem.
[0018] In Patent reference 2 (the second conventional technology),
if the material is exposed to the air in the PDP manufacturing
processes, the protective layer absorbs unnecessary components such
as CO.sub.2 and water, thereby changing the characteristics of the
protective layer. This deteriorates the secondary electron emission
efficiency, thereby increasing the discharge starting voltage and
narrowing the driving margin of the PDP.
[0019] With the technology of Patent reference 6, the secondary
electron emission factor .gamma. is estimated to be about 0.2 at
the maximum, which corresponds to a level obtain able by a
conventional protective layer made of MgO having one-layer
structure, although specific values for the secondary electron
emission efficiency and the discharge starting voltage generated by
using the two-layer protective layer structure are not disclosed in
Patent reference 6. Accordingly, the discharge starting voltage
according to Patent reference 6 is also estimated to be the same
high level as that achieved in the conventional technologies.
[0020] Furthermore, if the characteristic of the protective layer
changes, the discharge starting voltage while driving PDP would
vary to cause black noises and affect the display quality and
reliability.
[0021] A possible method for countering this problem is to perform
an evacuator process, before discharge gas enclosure, to remove gas
of adhered CO.sub.2 and water. However PDPs have a structure in
which a gap between the front panel and the back panel is narrow,
and so an evacuation conductance is extremely small. As a result,
the process takes comparatively long, and a different problem
relating to the process cost can arise.
[0022] As stated above, there remain problems concerning gas
discharge panels.
[0023] The present invention has been conceived in view of the
above-stated problems. The first object of the present invention is
to provide a gas discharge display panel that exhibits a favorable
display performance by maintaining a wall charge retaining power,
controlling discharge delay within a range adequate for optimal
image display, and reducing the discharge starting voltage at
comparatively low cost.
[0024] The second object of the present invention is to provide a
PDP that exhibits more reliability with enhanced display quality by
further improving the secondary electron emission factor .gamma.
compared to conventional cases and lowering the discharge starting
voltage to widen the driving margin. The second object of the
present invention is further to provide a manufacturing method of a
gas discharge display panel, by which the manufacturing cost lowers
by reduction of the exhaustion time in the sealing exhaustion
process, and by which the driving circuit cost is reduced.
MEANS TO SOLVE THE PROBLEMS
[0025] So as to solve the above-stated problems, the present
invention provides a gas discharge display panel including a
substrate, a dielectric layer, and a protective layer, the
dielectric layer and the protective layer being formed in the
stated order on a surface of the substrate, where the protective
layer contains H in a range of 300 mass ppm to 10000 mass ppm
inclusive with respect to a MgO content of the protective
layer.
[0026] Here, the H content of the protective layer may be in a
range of less than 1500 mass ppm with respect to the MgO
content.
[0027] Here, the protective layer may further contain Si in a range
of 20 mass ppm to 5000 mass ppm inclusive with respect to the MgO
content.
[0028] Or, the protective layer may further contain Ge in a range
of 10 mass ppm or above and below 500 mass ppm with respect to the
MgO content.
[0029] The present invention also provides a gas discharge display
panel including a substrate, a dielectric layer, and a protective
layer, the dielectric layer and the protective layer being formed
in the stated order on a surface of the substrate, in which when
the protective layer is subjected to a cathodoluminescence
spectroscopy, a relative are a intensity of a first intensity with
respect to a second intensity for a light emission peak are a is in
a range of 0.6 to 1.5 inclusive, where the first intensity is a
light emission peak intensity generated in a wavelength range of
720 nm or above and below 770 nm and the second intensity is a
light emission peak intensity generated in a wavelength range of
300 nm or above and below 450 nm.
[0030] Here, the protective layer may contain H in addition to
MgO.
[0031] In addition, a structure is possible in which the protective
layer contains H and Si in addition to MgO, where the Si content is
in a range of 20 mass ppm to 5000 mass ppm inclusive with respect
to the MgO content.
[0032] In addition, the present invention provides a gas discharge
display panel including a substrate, a dielectric layer, and a
protective layer, the dielectric layer and the protective layer
being formed in the stated order on a surface of the substrate, in
which when the protective layer is subjected to a
cathodoluminescence spectroscopy, a relative are a intensity of a
second intensity with respect to a third intensity for a light
emission peak are a is in a range of 0.9 or above, where the second
intensity is a light emission peak intensity generated in a
wavelength range of 450 nm or above and below 600 nm and the third
intensity is a light emission peak intensity generated in a
wavelength range of 300 nm or above and below 450 nm.
[0033] Here, the protective layer may contain H in addition to
MgO.
[0034] Furthermore, a structure is also possible in which the
protective layer contains H and Ge in addition MgO, where the Ge
content is in a range of 10 mass ppm to 300 mass ppm inclusive with
respect to the MgO content.
[0035] The protective layer may contain Ge in a range of 10 mass
ppm or above and below 300 mass ppm with respect to the MgO
content.
ADVANTAGEOUS EFFECT OF THE INVENTION
[0036] The inventors of the present invention have been dedicated
to finding a method of solving the conventional problem of
discharge delay in the address period. As a result, the inventors
have found that the problem is solved by making a protective layer
by including, in the main component of MgO, Si, or Ge respectively
in the above-defined content ratio, and optionally H.
[0037] According to the protective layer having the stated
structures, by the addition of the Si, Ge, and H respectively in an
adequate amount to MgO, it becomes possible to produce such
advantageous effects as enabling to control the discharge delay in
an optimal range without lowering the wall charge retaining power
at the time of driving, and to dramatically and effectively prevent
the occurrence of writing defect during the address period.
Furthermore, the protective layer having the stated structures also
lowers the discharge starting voltage.
[0038] In addition, the present invention has another advantage of
being realized in comparatively low cost, because of the structure
of merely adding Si, Ge, and optionally H respectively in an
adequate amount to MgO.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] The following describes embodiments the present invention,
with use of the drawings.
First Embodiment
[0040] 1-1. Structure of PDP
[0041] FIG. 1 is a partial perspective view showing a main
structure of an AC-type PDP 1, according to the first embodiment of
the present invention. In the drawing, the z-direction corresponds
to a thickness direction of the PDP 1, and the xy plane corresponds
to a plane parallel to the surface of the panels of the PDP 1.
Here, the PDP 1 has an NTSC specification of 42 inches for example.
However needless to say, the present invention is also applicable
to other specifications, including XGA, and SXGA. The present
invention is also applicable to other sizes.
[0042] As FIG. 1 shows, the PDP 1 is mainly structured by a front
panel 10 and a back panel 16 whose main surfaces are opposed to
each other.
[0043] On one main surface of the front panel glass 11 that is a
substrate of the front panel 10, a plurality of pairs of display
electrodes 12 and 13 (scan electrode 12 and sustain electrode 13)
are provided. Each display electrode 12, 13 is formed by stacking
bus lines 121 and 131 (having thickness of 7 .mu.m, and width of 95
.mu.m) made of an Ag thick film (having thickness of 2 .mu.m-10
.mu.m), an aluminum (Al) thin film (having thickness of 0.1 .mu.m-1
.mu.m), or a Cr/Cu/Cr thin film (having thickness of 0.1 .mu.m-1
.mu.m) onto belt-like transparent electrodes 120, 130 (having
thickness of 0.1 .mu.m, and width of 150 .mu.m) made of a
transparent conductive material such as ITO and SnO.sub.2. The bus
lines 121, 131 lower sheet resistance of the transparent electrodes
120, 130.
[0044] The front panel glass 11 provided with the display
electrodes 12, 13 is provided with a low-melting glass dielectric
layer 14 (having a thickness of 20 .mu.m-50 .mu.m) on an entire
main surface of the front panel glass 11 in a screen printing
method and the like. The dielectric layer 14 is mainly composed of
lead oxide (PbO), bismuth oxide (Bi.sub.2O.sub.3), or phosphorus
oxide (PO.sub.4). The dielectric layer 14 has a current control
function typical of an AC-type PDP, which helps obtain a long life
compared to a DC-type PDP. A protective layer 15 having a thickness
of about 1.0 .mu.m is coated on a surface of the dielectric layer
14.
[0045] The first embodiment is characterized by a structure of the
protective layer 15, which is detailed as follows.
[0046] On one main surface of the back panel glass 17 that is a
substrate of the back panel 16, a plurality of address electrodes
18 are arranged in a stripe formation with a distance (360 .mu.m)
therebetween in y-direction where x-direction is a lengthwise
direction. Each address electrode 18 has a width of 60 .mu.m and is
made of Ag thick film (thickness of 2 .mu.m-10 .mu.m), aluminum
(Al) thin film (thickness of 0.1 .mu.m-1 .mu.m), or Cr/Cu/Cr thin
film (thickness of 0.1 .mu.m-1 .mu.m). A dielectric layer 19 having
a thickness of 30 .mu.m is coated onto the back panel glass 17 so
as to cover the address electrodes 18.
[0047] Further on the dielectric layer 19, barrier ribs 20 (height
of about 150 .mu.m and width of 40 .mu.m) are provided in-between
the address electrodes 18. Cell SUs are divided by adjacent barrier
ribs 20, and function to prevent occurrence of erroneous discharge
or optical crosstalk in the x-direction. A corresponding one of
phosphor layers 21-23 is formed on side surfaces of each of the
barrier ribs 20 and a surface of the dielectric layer 19
therebetween, where the phosphor layers 21-23 respectively
correspond to red (R), green (G), and blue (B) for color
display.
[0048] It is alternatively possible to cover the address electrodes
18 directly with the phosphor layers 21-23, instead of the
dielectric layer 19.
[0049] The front panel 10 and the back panel 16 are provided to
oppose each other so that the lengthwise direction of the address
electrodes 18 is orthogonal to the lengthwise direction of the
display electrodes 12, 13. The circumference of the two panels 10
and 16 is sealed with a glass frit. Between the panels 10 and 16, a
discharge gas (sealing gas) made of an inert gas component such as
He, Xe, and Ne, and the like is sealed with a predetermined
pressure (normally approximately with a pressure of 53.2 kPa-79.8
kPa).
[0050] A discharge space 24 is formed between any two adjacent
barrier ribs 20. Each are a where a pair of display electrodes 12,
13 cross over one address electrode 18 with the discharge space 24
therebetween corresponds to one cell SU. Note that a cell is
occasionally called "sub-pixel", too. The pitch of a cell is 1080
.mu.m in x-direction and 360 .mu.m in y-direction. Three adjacent
cells SU each corresponding to RGB form one pixel (1080
.mu.m.times.1080 .mu.m).
[0051] 1-2. Driving Method of PDP
[0052] The PDP1 having the above-stated structure is driven in the
following way. A driving unit not illustrated in the drawings
applies an AC voltage of about some tens of kHz to some hundreds of
kHz to each gap created between a pair of display electrodes 12,
13, theregy generating discharge within the cells SU. Excited Xe
molecules emit ultraviolet light to excite the phosphor layers
21-23. As a result, visible light is emitted.
[0053] One example of the driving method is a field time-sharing
grayscale display method. In this display method, a display field
is divided into a plurality of subfields. Each subfield is further
divided into a plurality of periods. In each subfield, wall charge
accumulated in the entire screen is initialized (i.e. reset) during
the initialization period. In the address period, address discharge
is performed with respect to only discharge cells to be lit to
accumulate wall charge to the discharge cells to be lit. In the
discharge sustain period that follows, an alternating current
voltage (sustain voltage) is simultaneously applied to all the
discharge cells, to sustain discharge for a certain period of time.
In this way, light emission display is realized.
[0054] In this driving method, the driving unit divides each of the
fields F into six subfields for example for the purpose of
representing light emission in each cell by a binary control of
ON/OFF, where the fields F are arranged chronologically and are
images input from outside. Brightness of the subfields are weighted
so that the relative ratio will be for example 1:2:4:8:16:32,
thereby setting the number of times of light emission with respect
to sustain (sustain discharge) of each subfield.
[0055] Here, FIG. 2 is one example of a driving wave form process
of the present PDP1. FIG. 2 specifically shows a wave form of the
m-th subfield within the fields. As FIG. 2 shows, each subfield is
assigned an initialization period, an address period, a discharge
sustain period, and a deletion period.
[0056] The initialization period is for performing initialization
discharge, and is for deleting wall charge of the entire screen for
preventing an effect of prior illumination of each cell (i.e. for
preventing an effect from accumulated wall charge). In the wave
form example of FIG. 2, a reset pulse in a descending lamp wave
form of a positive polarity that exceeds the discharge start
voltage Vf is applied to all the display electrodes 12, 13.
Simultaneously, a positive-polarity pulse is applied to all the
address electrodes 18 for preventing charging and ion bombardment
from occurring at the back panel 16 side. By a voltage differential
between ascending and descending of an application pulse,
initialization discharge that specifically is a weak surface
discharge takes place in every cell, thereby accumulating wall
discharge in every cell. As a result, the entire screen will be
brought in a uniform charging state.
[0057] The address period is for performing addressing (i.e.
setting of illumination/non-illumination) to cells selected based
on an image signal divided into subfields. In this address period,
with respect to the ground potential, the scan electrodes 12 are
biased towards the positive potential, and the sustain electrodes
13 are biased towards the negative potential. While keeping this
state, a scan pulse of a negative polarity is applied to the scan
electrodes 12 one by one from the top line positioned in the upper
end of the panel, where each line corresponds to one horizontal
sequence of cells and also corresponds to one pair of display
electrodes. In addition, to address electrodes 18 that correspond
to cells to be lit, an address pulse of a positive polarity is
applied. With this arrangement, while inheriting the weak surface
discharge of the initialization period, address discharge is
performed only in the cells to be lit, thereby accumulating wall
charge.
[0058] The discharge sustain period is for sustaining discharge,
for the purpose of assuring the brightness in accordance with
grayscale, by enlarging the illumination state set in advance by
the address discharge. Here, all the address electrodes 18 are
biased to a positive potential for preventing unnecessary
discharge. At the same time, a sustain pulse of a positive polarity
is applied to all the sustain electrodes 13. Thereafter, a sustain
pulse is alternately applied to the scan electrodes 12 and the
sustain electrodes 13, so as to repeat discharge for a certain time
period.
[0059] The deletion period is for deleting the wall charge by
applying a declining pulse to the scan electrodes 12.
[0060] Note that the lengths of the initialization period and the
length of the address period are respectively constant regardless
of the brightness weight. Meanwhile the length of the discharge
sustain period is longer as the weight of the brightness gets
larger. In other words, the length of display period is different
among the subfields.
[0061] In the PDP1, vacuum ultraviolet light composed of a
resonance line having an acute peak at 147 nm attributable to Xe
and molecule lines centered around 173 nm are generated. The vacuum
ultraviolet light is irradiated onto each of the phosphor layers
21-23, thereby generating visible light. Then by a combination of
each color of RGB in each subfield, a display in multicolor and
multi-grayscale is realized.
[0062] The first embodiment is characterized by a structure of the
protective layer 15 in the PDP1.
[0063] The protective layer 15 in the first embodiment is mainly
composed of MgO. Besides, the protective layer 15 contains impurity
(dopant) of Si in the range of 20 mass ppm to 5000 mass ppm
inclusive, and H in the range of 300 mass ppm to 10000 mass ppm
inclusive. According to the structure of the protective layer 15
that includes a predetermined amount of the mentioned impurity, the
PDP1 is able to have an increased amount of electrons from the
protective layer 15 which would contribute to discharge, thereby
realizing an effect of restricting occurrence of discharge delay.
In addition, even if the discharge delay is caused, variation in
time of delay is restrained, which would lead to realization of an
excellent image display performance.
[0064] As follows, this characteristic is described in greater
detail.
[0065] <Characteristic and Advantageous Effect of First
Embodiment>
[0066] Conventional PDPs sometimes cannot obtain an adequate image
display attributable to writing defect based on the discharge delay
in the address period while being driven. However the PDP of the
present invention is able to solve this problem effectively by
adding H to MgO that constitutes the protective layer, and
optionally adding thereto Si or Ge in an adequate amount, as stated
above.
[0067] To be more specific, in the present invention, occurrence of
discharge delay is restrained by promoting emission of electrons
from the protective layer that contribute to discharge, and the
retaining power of the wall charge is maintained thereby
restraining writing defect. As a result, address discharge and
succeeding sustain discharge are normally executed, thereby
realizing a favorable image display performance.
[0068] In addition, if the discharge delay is caused in the present
invention while the PDP is being driven, the variation in discharge
delay time (discharge variability) is restrained compared to
conventional PDPs, and the level of discharge variability is
averaged. By alleviating the discharge variability in this way, the
present invention has another advantageous effect of effectively
preventing the occurrence of writing defect due to discharge delay
in a drastic manner, by adopting measures such as delaying a timing
of pulse application during the address period for the entire panel
for a predetermined time period for example.
[0069] Accordingly, the PDP1 of the present invention is able to
perform assured addressing, and so can perform addressing with a
favorable probability with even a little smaller application pulse
width during the address period. This further means that even
without adopting a conventional dual scan method, a favorable
driving is enabled by adopting a driving method such as a so-called
single scan method which is mandated to reduce the number of driver
IC to half. For this reason, the present invention has other
advantages such as simplifying the structure of the driving unit
and realizing production at low cost.
[0070] The present invention produces advantageous effects of
restraining discharge variability, and of further realizing both of
restraining of discharge delay and maintaining the retaining power
of wall charge, which can not be realized by the conventional
technologies such as Patent references 3, 4, and 5. The inventors
of the present invention have found the above-described structure
as an effective solution by performing examination in view of how
to cope with such problems of discharge variability, discharge
delay, and wall charge retaining power maintenance.
[0071] Next, data obtained in performance comparison tests using
embodiment examples is detailed as follows.
[0072] <Embodiment Examples and Confirmation Test for
Advantageous Effect Thereof>
[0073] FIG. 3 illustrates a graph for showing compositions of a
protective layer and a relative size of a variation in discharge
delay time (discharge variability). In this drawing, data relating
to protective layers having the following structures is presented
with the discharge variability of a conventional protective layer
solely made of MgO being assumed as 100%.
[0074] Si added protective layer (comparison example 2): [0075] 100
mass ppm of Si is added to MgO.
[0076] Si+H added protective layer (first embodiment): [0077] 100
mass ppm of Si, and 1000 mass ppm of H are added to MgO.
[0078] H added protective layer (second embodiment): [0079] 1000
mass ppm of H is added to MgO.
[0080] From the data in FIG. 3, the protective layer (comparison
example 2) with only Si addition in comparatively a small amount to
MgO is considered as undesirable because the value of discharge
variability is 114% which indicates performance deterioration even
compared to the conventional case. The comparison example 2
corresponds in structure to Patent reference 7 described above. The
data also shows that the technology of Patent reference 3 is not
suitable in obtaining favorable image display performance in
reality.
[0081] On the other hand, the embodiment example 1 (first
embodiment) in which a predetermined amount of Si and a
predetermined amount of H is added to MgO is able to restrain
discharge variability approximately down to 31% with respect to the
comparison example 1. This confirms that the embodiment example 1
has an effect of averaging the discharge delay time among a
plurality of cells. Furthermore, in a case (embodiment example 2)
where the protective layer is created by adding only H in a
strictly defined amount to MgO, an effect of reducing the discharge
variability approximately down to 54% was obtained with respect to
the comparison example 1. This confirms that the embodiment example
2 also produces a sufficient level of the advantageous effect of
the present invention.
[0082] FIG. 4 shown next illustrates intensity of discharge
variability for each of a conventional protective layer made only
of MgO (i.e. comparison example "a", or the comparison example 1),
comparison examples "b" and "c", in which a predetermined amount of
Si is added to MgO, and embodiment examples "d" "e" "f" "g" and "h"
in which a predetermined amount of H and optionally a predetermined
amount of Si are added.
[0083] In the embodiment examples and the comparison examples shown
in FIG. 4, the embodiment example f which contains 100 mass ppm of
Si and 1000 mass ppm of H is confirmed as the best structure in
restraining the discharge variability. As the content of Si gets
larger than in this embodiment example f, it is confirmed that the
discharge variability increases (e.g. as shown in embodiment
examples g and h). Accordingly, so as to obtain higher performance
than the comparison example a in the context of the present
invention, adequate content of H and optionally Si with respect to
MgO should be defined. The specific ranges of H and Si are detailed
later.
[0084] As is clear from the test results, it is expected that the
structure of the present invention produce an effect of alleviating
the discharge variability and averaging the level of discharge
variability compared to the conventional cases. As a result, even
if discharge delay is caused in the address period, it is still
possible to perform assured addressing either by delaying the
application timing of address pulse or setting a pulse width in
concurrence with the discharge delay time, thereby realizing a
favorable image display performance.
[0085] Next, FIG. 5 is a graph showing a composition of the
protective layer, discharge delay (in relative value), and a wall
charge retaining power index. In this drawing, the discharge delay
and the wall charge retaining power index are assumed to be 1 under
a condition that the image quality does not have any practical
problem. In addition, if the discharge delay is 1 or below, and if
the wall charge retaining power index is 1 or above, the image
quality is assumed to be within an allowable range. In other words,
a product is considered favorable when the following conditions are
satisfied: "discharge delay <1" and "wall charge retaining power
index >1". Data shown in FIG. 5 relates to the protective layers
having the following structures respectively.
[0086] Conventional MgO (comparison example 1): [0087] MgO with no
impurity addition
[0088] H-added MgO (Comparison example 2): [0089] 2000 mass ppm of
H is added to MgO
[0090] H+Ge-added MgO (Embodiment example 1): [0091] 50 mass ppm of
Ge and 2000 mass ppm of H are added to MgO
[0092] Ge-added MgO (1) (embodiment example 2): [0093] 50 mass ppm
of Ge is added to MgO
[0094] Ge-added MgO (2) (comparison example 3): [0095] 1000 mass
ppm of Ge is added to MgO
[0096] From the data of FIG. 5, in the protective layer (comparison
example 2) produced by adding only H to MgO, discharge delay is
restrained, but the wall charge retaining power is deteriorated.
Accordingly, a protective layer having this structure is considered
undesirable because of having comparatively lowered performance.
This comparison example 2 corresponds in structure to Patent
reference 4. From the data, it is understood that favorable image
display performance is not expected in reality from the technology
of Patent reference 4.
[0097] On the other hand, with the embodiment example 1 (first
embodiment) in which H in a predetermined amount and Ge in a
predetermined amount are added to MgO, the discharge delay caused
is within the optimal range with respect to the image display, and
has not experienced any practical problem with respect to the wall
charge retaining power either.
[0098] In addition, if a protective layer is structured by adding
only Ge in a strictly defined amount to MgO (embodiment example 2),
it is confirmed that the effect of the present invention is
sufficiently realized.
[0099] However, in a case where a protective layer is produced by
adding only 1000 mass ppm of Ge to MgO (comparison example 3), the
discharge delay exceeds the allowable range for obtaining favorable
images, as FIG. 5 shows. This means that the probability of
generating address discharge during the address pulse application
is lowered, which would likely lead to writing defect.
[0100] As is clear from the above test results, the structure of
the present invention enables to control display delay within the
optimal range for image display while maintaining the wall charge
retaining power. As a result, it becomes possible to obtain a
favorable image display performance by preventing occurrence of
writing defect during the address period. The necessary content of
H and Ge in the present invention is detailed later.
[0101] Next, with respect to protective layers 15 having different
discharge variability, a cathode luminescence is measured during
PDP driving, and a relation between light emission spectrum and
discharge variability which is peculiar to the protective layer, is
examined. The cathodoluminescence (CL) spectroscopy is an analysis
method for detecting a light emission spectrum as an energy
alleviating process incident to irradiation of an electron to a
sample, thereby knowing whether there is any defect within the
sample (i.e. protective layer) and information such as its
structure.
[0102] FIG. 6 shows data regarding the test results of the
cathodoluminescence spectroscopy. FIG. 6 is for showing a relation
between a light emission wavelength and light emission intensity,
with the horizontal axis representing a light emission wavelength,
and the vertical axis representing light emission intensity. The
samples are specifically as follows:
[0103] Sample A: (MgO+Si+H), embodiment example
[0104] Sample B: (MgO+400 mass ppm of H)
[0105] Sample C: (only MgO)
[0106] Sample D: (MgO+1000 mass ppm of Si)
[0107] The measurement conditions are as follows.
[0108] Electron accelerating voltage: 5 kV
[0109] Filament current density: 2.4.times.10.sup.8
(A/cm.sup.2)
[0110] FIG. 6 shows relative values of discharge variability 31,
74, 100, and 184, respectively for the samples A, B, C, and D in
the stated order, with a respective spectrum wave form for a
corresponding protective layer. For each spectrum, substantially
three peaks (light emission wavelength of about 410 nm, about 510
nm, and about 740 nm) are observed. The value of wavelength for
each peak is correlated with defective energy existing in the band
gap of the protective layer. From this relation, it is understood
that, as the light emission wavelength at about 740 nm gets larger,
a larger number of electrons is emitted from the protective layer
that contribute to discharge, and that the expected effect of
restraining the discharge variability is large.
[0111] Note that only a relative value of the luminous intensity in
the context of each wave form has meaning, and an absolute value of
the luminous intensity does not have any special meaning.
[0112] For each protective layer of the embodiment examples
(samples A and B), a clear peak is observed for each light emission
wavelength. In particular, the peaks at about 740 nm light emission
wavelength are larger for the samples A and B than those for the
other samples C and D. From this, it is estimated that even if a
protective layer contains Si in addition to MgO, if the amount of
Si is not adequate, the protective layer cannot produce an optimal
effect. The same thing applies to a protective layer that contains
H.
[0113] Next, FIG. 7 shows a relation between the discharge
variability of a protective layer and a relative are a intensity at
a peak light emission wavelength of about 740 nm relative to the
peak intensity at a peak light emission wavelength of about 410 nm,
regarding the cathodoluminescence spectroscopy. From the left of
the horizontal axis corresponding to small discharge variability,
data respectively of samples A, B, C, and D is shown in this
order.
[0114] As can been seen from the relative are a intensity for the
samples A and B in FIG. 7, the value of the relative are a
intensity should be desirably in the range of 0.6 to 1.5,
inclusive, for the purpose of obtaining smaller discharge
variability than in the conventional structures (samples C and D).
If the relative are a intensity becomes 1.5 or above, the carrier
concentration of the protective layer becomes too large thereby
reducing the insulation resistance. This is not desirable because
then the retaining power of wall charge is expected to
decrease.
[0115] Note that the wavelength inherently has variations to some
extent. Therefore in reality, suppose classifying the light
emission peak intensity generated in the wavelength range of 720 nm
to 770 nm inclusive as a first intensity, and the light emission
peak intensity generated in the wavelength range of 300 nm to 450
nm inclusive as a second intensity. Then it is desirable that the
relative are a intensity of the first intensity with respect to the
second intensity for the light emission peak are a is in the range
of 0.6 to 1.5 inclusive.
[0116] FIG. 8 shows a relation between a discharge starting voltage
of a protective layer and relative are a intensity of the peak
light emission wavelength at about 510 nm with respect to the peak
light emission wavelength at about 410 nm, regarding the
cathodoluminescence spectroscopy. From the left of the horizontal
axis corresponding to small discharge starting voltage, samples are
shown in the order shown below:
[0117] Sample E: (MgO+50 mass ppm of Ge+1200 mass ppm of H)
[0118] Sample F: (MgO+50 mass ppm of Ge)
[0119] Sample G: (MgO+1200 mass ppm of H)
[0120] Sample H: (only MgO, conventional structure)
[0121] The measurement conditions are as follows.
[0122] Electron accelerating voltage: 5 kV
[0123] Filament current density: 6.3.times.10.sup.5
(A/cm.sup.2)
[0124] Here, the reason why the current density is different from
the measurement conditions of FIGS. 6 and 7 is that the present
measurement of FIG. 8 is performed using a different apparatus, and
so the spot diameter of the electrons differs largely from the
example of FIGS. 6 and 7.
[0125] As is understood by FIG. 8, if the value of the relative are
a intensity is 0.9 or above, the discharge starting voltage is
reduced compared to the conventional structure (i.e. sample D).
Note that the wavelength inherently has variations to some extent.
Therefore in reality, suppose classifying the light emission peak
intensity generated in the wavelength range of 450 nm or above and
below 600 nm as a second intensity, and the light emission peak
intensity generated in the wavelength range of 300 or above and
below 450 nm as a third intensity. Then it is desirable that the
relative are a intensity of the second intensity with respect to
the third intensity is in the range of 0.9 or above.
[0126] Furthermore, as long as the relative are a intensity is 0.9
or above for the protective layer of the present invention, the
same effect as stated above is expected regardless of whether the
dopant is a combination of Ge and H, or solely Ge.
[0127] Concretely, the same effect is expected for a protective
layer in which H is diffused in MgO with respect to the Ge content
that is in the range of 10 mass ppm to 300 mass ppm inclusive, or a
protective layer in which only Ge in the range of 10 mass ppm or
above and below 300 mass ppm is diffused in MgO. Data regarding
such an embodiment example of adding an adequate amount of Ge to
MgO is shown as the embodiment example 2 in FIG. 5.
[0128] Next, the amount of H and Si necessary in the present
invention is detailed below.
<Amount of H and Si to be added with respect to MgO>
[0129] Next, the following shows the result of examinations
performed by the inventors of the present invention regarding the
components of the protective layer from which the effect of the
present invention is obtain able effectively.
[0130] Here, the content of Si in the protective layer 15 can be
examined by a secondary ion mass spectrometry method (SIMS
method).
[0131] On the other hand, the content of H in the protective layer
15 can be examined using a hydrogen forward scatting method (HFS
method).
[0132] As stated above, discharge variability is examined by
changing the contents of H and Si to be added. As a result, in the
protective layer that contains both of Si and H in addition to MgO,
the content of the Si is preferably in the range of 20 mass ppm to
10000 mass ppm inclusive.
[0133] Furthermore, it is confirmed that, if the content of Si is
in the range of 50 mass ppm to 1000 mass ppm inclusive, the effect
of restraining discharge variability is particularly prominent.
From FIG. 4, discharge variability is small in the embodiment
examples f, g, and h that respectively have a Si content of 100
mass ppm, 500 mass ppm, and 1000 mass ppm. Consequently, discharge
variability is considered small if the content of Si is in the
range of 50 mass ppm to 1000 mass ppm inclusive.
[0134] When the Si content is smaller than 20 mass ppm, it is
confirmed that the discharge delay restraining effect is extremely
small. Conversely, if the Si content becomes larger than 5000 mass
ppm, the discharge variability becomes extremely large, and
crystallinity of the protective layer is confirmed to be adversely
affected according to the result of the x-ray diffraction
measurement method and the like.
[0135] On the other hand, as a result of the examination using the
HFS, it is confirmed that the H content to be added together with
silicon in the above-stated structure of the protective layer is
desirably in the range of 300 mass ppm to 10000 mass ppm
inclusive.
[0136] Note that when the Si content becomes smaller than 20 mass
ppm, it is confirmed that the discharge delay restraining effect
gets extremely small. Conversely, if the Si content becomes larger
than 5000 mass ppm, the discharge variability becomes extremely
large, and that crystallinity of the protective layer is confirmed
to be adversely affected according to the result of the x-ray
diffraction measurement method and the like.
[0137] Furthermore, it is confirmed that the H content in the range
of 1000 mass ppm to 2000 mass ppm, inclusive is preferable, for the
discharge delay restraining effect is in particular obtain
able.
[0138] Additionally in this case, if the H content becomes smaller
than 300 mass ppm, it is undesirable because the effect of H
addition becomes extremely small. Conversely, if the H content
becomes larger than 10000 mass ppm, it is also undesirable because
the carrier concentration of the protective layer becomes too large
to degrade the insulation resistance, and further to degrade the
wall charge retaining power.
[0139] Furthermore, in the present invention, the protective layer
in which an adequate amount of H is added to MgO just as in the
embodiment examples d and e in FIG. 4 obtains substantially the
same effect as the effect obtained by the protective layer that
contains a predetermined amount of Si and a predetermined amount of
H.
[0140] The above data shows that the preferable amount of H atoms
to be added to MgO together with Si is in the range of 300 mass ppm
to 10000 mass ppm inclusive.
[0141] Next, the amount of H and Ge to be added in the protective
layer, which is necessary in the present invention, is detailed
below.
[0142] <Amount of H and Ge to be Added with Respect to
MgO>
[0143] Next, the following shows the result of examinations
performed by the inventors of the present invention regarding the
components of the protective layer from which the effect of the
present invention is effectively obtain able.
[0144] Here, the content of Ge in the protective layer 15 can be
examined by a secondary ion mass spectrometry method (SIMS
method).
[0145] On the other hand, the content of H in the protective layer
15 can be examined using a hydrogen forward scatting method (HFS
method).
[0146] First, examination is performed based on the SIMS. The
result shows that for the protective layer in which both Ge and H
are added to MgO, the preferable range of the Ge content is 10 mass
ppm or above and below 500 mass ppm.
[0147] Furthermore, if the Ge content is within the range of 20
mass ppm to 100 mass ppm inclusive, it is confirmed that the image
display quality is particularly excellent.
[0148] Note that if the Ge content becomes smaller than 10 mass
ppm, it is confirmed that the wall charge retaining power becomes
extremely small. Conversely, if the Ge content becomes larger than
500 mass ppm, the discharge delay becomes extremely large, and the
crystallinity of the protective layer is confirmed to be adversely
affected according to the result of the x-ray diffraction
measurement method and the like.
[0149] On the other hand, examination based on the HFS reveals that
the preferable range of the H content to be added with Ge in the
protective layer having the above-mentioned structure is 300 mass
ppm to 10000 mass ppm inclusive.
[0150] The result further shows that if the H content is in the
range of 1000 mass ppm to 2000 mass ppm inclusive, it is preferable
since the effect of restraining discharge delay occurrence is
particularly obtain able.
[0151] In this case, if the H content becomes smaller than 300 mass
ppm, it is undesirable because the effect of H addition becomes
extremely small. Conversely, if the H content becomes larger than
10000 mass ppm, it is also undesirable because the carrier
concentration of the protective layer becomes too large to degrade
the insulation resistance, and further to degrade the wall charge
retaining power.
[0152] So far, the description has been restricted, as embodiment
examples, to protective layers in which H and either Si or Ge are
added to MgO. However, the present invention may alternatively take
a structure in which only H is added to MgO, and in which the H
atom content is set in the range of 300 mass ppm to 10000 mass ppm
inclusive. Furthermore, in the protective layer in which only H is
added to MgO, another experimental data reveals that that it is
desirable to set an amount of H atoms to be added in the range of
300 mass ppm or above and less than 1500 mass ppm.
[0153] <Manufacturing Method of PDP>
[0154] As follows, one example of manufacturing methods of PDP 1
according to the first embodiment is described. The following
explanation also includes an example method of forming a protective
layer of the present invention.
[0155] (Manufacturing Front Panel)
[0156] Display electrodes are formed on a surface of the front
panel glass made of soda lime glass having a thickness of about 2.6
mm.
[0157] The following shows a method that uses a printing method.
However a dye coating method, or a blade coating method may also be
used.
[0158] An ITO (transparent electrode) material is applied on the
front panel glass in a predetermined pattern, and is dried. On the
other hand, a photosensitive paste is created by mixing a
photosensitive resin (i.e. photodegradable resin) to metal (Ag)
powders and the organic vehicle. This photosensitive paste is
applied onto the transparent electrode material, and is covered
with a mask having a pattern of the display electrodes to be
formed. Light exposure is performed over the mask, and then a
development process is performed. Then, a burning process is
performed at a burning temperature of about 590-600 degrees
Celsius. As a result, bus lines are formed on the transparent
electrodes. According to this photomask method, the bus lines can
be made thin to the level of a line width of about 30 .mu.m,
compared to a conventional screen printing method by which a line
width of 100 .mu.m is the thinnest. Note that the metal material of
the bus lines may be alternatively Pt, Au, Ag, Al, Ni, Cr, tin
oxide, and indium oxide, for example.
[0159] In addition, the electrodes are also formable by forming a
film using an electrode material using an evaporation method, a
sputtering method, and the like, and then by performing etching.
Next, above the formed display electrodes, a paste created by
mixing dielectric glass powders mainly made of oxide lead or
bismuth oxide having a softening temperature in the range of
550-600 degrees Celsius and an organic binder made of butyl
carbitol acetate and the like is applied, and is baked at a
temperature of about 550-650 degrees Celsius, thereby completing a
dielectric layer.
[0160] Next, on the surface of the dielectric layer, a protective
layer having a predetermined thickness is formed by an EB (electron
beam) evaporation method. In this way, the protective layer 15
containing an adequate amount of Si or Ge of the present invention
is formed by the EB evaporation method.
[0161] The source used in the evaporation for forming the
protective layer is for example prepared by mixing a Si compound or
a Ge compound either in pellet or powder form, with MgO in pellet
form, for example. It is also possible to prepare a source by
mixing MgO in powder form with either a Si compound or a Ge
compound in powder form. Still alternatively, the mentioned
mixtures may be sintered before completion. The concentrations of
the Si compound and the Ge compound are respectively set as
20-10000 mass ppm and 5-700 mass ppm. Then in the oxygen
atmosphere, the evaporation source is heated using a pierce-type
electron beam gun as a heating source to form a desired film. Here,
the electron beam current amount, oxygen partial pressure amount, a
substrate's temperature, and the like used in forming the film
hardly affects the composition of a resulting protective layer, and
therefore can be set arbitrarily.
[0162] Once the film made of MgO is formed, in an atmosphere
containing H, the MgO film is subjected to plasma processing. For
example, in a doping chamber of H atoms, a substrate is heated
using a heater to 100-300 degrees Celsius, and the chamber is
evacuated until the vacuum level reaches
7.times.10.sup.4-7.times.10.sup.-4 Pa. After this, Ar gas is
introduced while controlling the vacuum level to 6.times.10.sup.-1
Pa. Next, while introducing H gas at a current amount of
1.times.10.sup.-5-3.times.10.sup.-5 m.sup.3/min, a high frequency
source is used to apply a high frequency of 13.56 MHz thereby
generating discharge within the doping chamber of H atoms.
[0163] Then, plasma is generated by exciting H atoms by means of
this discharge. Then the protective layer 15 already, formed on the
substrate is exposed to the excited H for 10 minutes, thereby
performing H atom doping to the protective layer 15.
[0164] Note that the layer forming method is not limited to the EB
(electron beam) evaporation method, and may alternatively be a
sputtering method, and an ion plating method, for example.
[0165] The front panel completes as a result of the above-described
processes.
[0166] (Manufacturing Back Panel)
[0167] Address electrodes having a thickness of about 5 .mu.m are
formed on a surface of the back panel glass made of soda lime glass
having a thickness of about 2.6 mm, by applying a conductive
material mainly composed of Ag using a screen printing method in
stripe formation with a predetermined distance therebetween. Here,
so as to have the PDP 1 to comply with the NTSC standard or VGA
standard of 40-inch classes, it is required to set a distance
between adjacent address electrodes as about 0.4 mm or below.
[0168] Next, a glass paste mainly made of lead is applied with a
thickness of about 20-30 .mu.m on an entire surface of the back
panel glass to which the address electrodes have been formed, and
then baked, thereby completing a dielectric layer.
[0169] Next, using the same lead glass material as is used for the
dielectric layer, barrier ribs having a height of about 60-100
.mu.m are formed between the adjacent address electrodes. The
barrier ribs are for example formed by repeatedly applying the
paste containing the glass material using a screen printing method,
and thereafter baking it. Note that in the present invention, it is
desirable to include a Si component in the lead glass material
making the barrier ribs, for the purpose of restraining the
impedance increase of the protective layer. This Si component may
either be included in the chemical composition of the glass or
added to the glass material. In addition, an adequate amount of an
impurity (dopant) (e.g. N, H, Cl, F) having high vapor pressure may
be added in gas form, in the vapor phase while forming an MgO
film.
[0170] After the barrier ribs complete, a phosphor ink containing
one of red (R) phosphor, green (G) phosphor, and blue (B) phosphor
is applied on side surfaces of adjacent barrier ribs and a surface
of the dielectric layer exposed between the barrier ribs, and is
dried and baked, thereby completing a phosphor layer.
[0171] One example of the chemical composition of the phosphor
having colors of RGB is as follows:
[0172] Red phosphor: Y.sub.2O.sub.3, Eu.sup.3+
[0173] Green phosphor: Zn.sub.2SiO.sub.4:Mn
[0174] Blue phosphor: BaMgAl.sub.10O.sub.17:Eu.sup.2+
[0175] Each phosphor material has an average particle diameter of
2.0 .mu.m for example. A corresponding one of such phosphor
material is placed in a server in a ratio of 50 mass %. In the
server, 1.0 mass % of ethyl cellulose and 49 mass % of a solvent
(.alpha.-terpineol) are also thrown. The mixture is then subjected
to agitation mixture using a sand mill, thereby completing a
phosphor ink of 15.times.10.sup.-3 Pas. Then the phosphor ink is
injected from a nozzle having a diameter of 60 .mu.m using a pump,
so as to be applied in-between adjacent barrier ribs 20. During
this operation, the panel is moved in the lengthwise direction of
the barrier ribs 20, to facilitate application of the phosphor ink
in stripe formation. After this operation, the resulting panel is
baked at the temperature of 500 degrees Celsius for ten minutes,
thereby completing the phosphor layers 21-23.
[0176] The back panel completes as a result of the above-described
processes.
[0177] Note that the front panel glass and the back panel glass are
described above as being made of soda lime glass. However this is
one example, and other materials may be used.
[0178] (Completing PDP)
[0179] The front panel glass and the back panel glass manufactured
as above are attached to each other using glass for sealing. After
this, the discharge space is evacuated to a level of high vacuum
state (1.0.times.10.sup.-4 Pa), and discharge gas of Ne--Xe,
He--Ne--Xe, Ne--Xe--Ar, or the like is enclosed with a
predetermined pressure (here, a pressure of 66.5 kPa-101 kPa).
[0180] The PDP 1 completes as a result of the above processes.
Next, modification examples of forming the protective layer, which
are different from the above-described example method, are listed
as follows, regarding the manufacturing method of the PDP.
Modification Example 1
[0181] In the present modification example 1, first, a film mainly
composed of MgO and additionally containing Si or Ge is formed
using the method described in the first embodiment.
[0182] Then, means for generating H ion is used as a method of
doping the H atoms to the film, thereby irradiating H ion on the
surface of the formed film.
[0183] Here, the setting conditions are as follows for example:
using a heater, the substrate is heated to the temperature of
100-300 degrees Celsius within the doping chamber of H atoms, and
the chamber is evacuated until the vacuum level reaches
1.times.10.sup.-4-7.times.10.sup.-4 Pa.
[0184] After this, H ions are irradiated onto the protective layer
15 having been formed on the substrate using an ion gun linked to
the H container, thereby doping H atoms of the protective layer 15.
The amount of flowing for H is set in the range of
1.times.10.sup.-5-3.times.10.sup.-5 m.sup.3/min.
Modification Example 2
[0185] In the modification example 2, first a film made of MgO is
formed using the method described in the first embodiment. Then the
formed film is placed in a chamber. While the film is being
subjected to plasma processing in the atmosphere containing H, and
an evaporation source created by mixing a Si compound and a Ge
compound is heated using an electron beam gun, thereby completing a
protective layer containing H and either Si or Ge.
Modification Example 3
[0186] In the modification example 3, first, a film made of MgO is
formed using the method described in the first embodiment. Then the
formed film is placed in a chamber. While H ion is being irradiated
to the substrate using an ion gun linked to an H container, an
evaporation source created by mixing a Si compound and a Ge
compound is heated using an electron beam gun, thereby completing a
protective layer containing H and Si.
[0187] <Other Notes>
[0188] The forming method of the protective layer of the gas
discharge display panel according to the present invention is not
limited to each of the examples stated above, and other methods
such as a sputtering method and an ion plating method or the like
may be alternatively used.
Second Embodiment
[0189] FIG. 9 is a sectional conceptual diagram showing a structure
around a front panel of a PDP according to the second embodiment.
The basic structure of the PDP is the same as that described in the
first embodiment, except that the structure of the protective layer
15 is different therebetween. In the second embodiment, the
protective layer 15 has a first protective film 151 and a second
protective film 152 that is laminated on the first protective film
151, where the first protective film 151 contains impurity in
larger amount than the impurity contained in the second protective
film 152 that is genuine. "Impurity" here is for example H, Cl, and
F, which is able to activate MgO by forming a dangling bond. The
film thickness of the first protective film 151 is about 600 nm and
the film thickness of the second protective film 152 is about 30
nm, for example.
[0190] The first protective film 151 manufactured in this way is
more activated than in conventional cases, and is a little more apt
to absorb gas that contains unnecessary component such as carbon
incorporated during the manufacturing processes than in
conventional cases. However, the first protective film 151 is
expected to improve the secondary electron emission factory
compared to the conventional cases. As a result, the first
protective film 151 is expected to improve the performance. In
other words, since being an activated film formed by doping a MgO
film with a large amount of impurity, the first protective film 151
has an improved secondary electron emission efficiency compared to
a conventional protective layer made of MgO, and is further able to
decrease a discharge starting voltage.
[0191] As stated above, a protective layer 15 in the present
embodiment is formed by a first protective film 151 and a second
protective film 152 that is laminated onto an entire surface of the
first protective film 151. In addition, the first protective film
151 is larger in impurity content than the second protective film
152. As a result, during processes performed in the atmospheric
air, the protective layer 15 is prevented from absorbing gas
containing unnecessary component, and the discharge starting
voltage is reduced in large amount to widen the driving margin,
thereby enabling the PDP to exhibit more reliability with enhanced
display quality free from black noise.
[0192] In fact, the experiments conducted using embodiment examples
created according to the second embodiment reveal as follows. The
protective layer 15 of the PDP has a further improved secondary
electron emission efficiency compared to a protective layer of the
conventional one-layer structure or to a protective layer of the
two-layer structure disclosed in Patent reference 1. In fact, the
protective layer 15 according to the second embodiment has a
secondary electron emission factor .gamma. of about 0.3, and a
discharge starting voltage of about 120V where the conventional
value thereof is 180V, which proves enlargement of a driving
margin.
[0193] Furthermore, the PDP having the above-stated protective
layer is proved to have a reduced variation in discharge starting
voltage of the discharge cells and have a largely reduced display
defect attributable to black noise.
[0194] Another confirmation test regarding the second embodiment is
described as follows. FIG. 12 shows a result of XPS data obtained
by examining water absorption content of the protective layer
mentioned above (herein after "protective layer 1") after being
left to stand in the atmospheric air, where the MgO film of the
protective layer is controlled to incorporate impurity therein. In
the example of FIG. 12, another protective layer (herein after
"protective layer 2") whose MgO film is of high purity in a sense
of incorporating no impurity therein is also used for comparison
purposes. The test was conducted by leaving to stand these two
protective layers 1 and 2 in the atmospheric air, or by performing
thermal processing to the two protective layers 1 and 2 at the
temperature of 500 degrees Celsius for two hours.
[0195] As is clear from FIG. 12, the water absorption content of
the protective layer 1 incorporating impurity therein is larger
than that of the protective layer 2 incorporating no impurity
therein. From this result, it is considered possible to carry out
the present invention stated above with more effectiveness and
stability, by means of the following embodiment examples that
attempt to solve the problem of gas absorption.
[0196] (Manufacturing Method)
[0197] An example of the manufacturing processes of the protective
layer 15 according to the second embodiment is explained as
follows.
[0198] Overall, the protective layer 15 is manufactured by forming
a first protective film 151 made of MgO on an entire surface of the
dielectric layer 14 with use of a sputtering method that is used
for the first embodiment, an electron beam evaporation method, or a
CVD (chemical vapor deposition) method, and then by forming a
second protective film 152 made of metal oxide being a high purity
MgO to cover an entire surface of the first protective film 151.
[0199] (a) First of all, display electrodes 12, 13 are provided on
a surface of the front panel glass 11. Then a dielectric layer is
formed onto the surface of the front panel glass 11 to cover the
display electrodes 12, 13. [0200] (b) After this process, Ar ions
in plasma state are sputtered to MgO target, using a sputtering
apparatus. As a result, a first protective film 151 with a film
thickness of about 600 nm is formed on a surface of the dielectric
layer 14.
[0201] In the manufacturing process (b), by forming the first
protective film 151 while introducing H.sub.2 gas into the Ar gas,
H is doped as impurity in the first protective film 151. As a
result, the MgO film that is to be the first protective film 151 is
activated by means of formation of so-called dangling bond, and the
secondary electron emission factor .gamma. improves compared to the
other are as of the protective layer (i.e. or compared to a
protective layer having a conventional structure).
[0202] Here, "dangling bond" is unsaturated bond of an atom group
that surrounds a certain lattice defect ("oxygen defect" in this
case) found in the vicinity or inside a film surface. The dangling
bond is apt to catch or absorb an impurity gas atom such as
electrons and carbons generated during a manufacturing process.
Note here that the adequate range of H impurity content in the
first protective film 151 is 1.times.10.sup.18-23/cm.sup.3. The
impurity dope amount should be taken care of. If the impurity dope
amount becomes too small, the secondary electron emission factor
.gamma. goes down to the conventional level. On the contrary, if
the impurity dope amount becomes too large, the film resistance
becomes too low, to make it hard to retain wall charge that
corresponds to written data. [0203] (c) Next, in the sputtering
apparatus, the high impurity MgO target is sputtered by means of Ar
gas, thereby forming the second protective film 152, being a MgO
film, with a film thickness of about 30 nm. According to this
method, the resulting second protective film 152 does not absorb so
much gas that contains unnecessary components during the processes.
Such a second protective film 152 is able to greatly reduce the
amount of impurity emitted between the panels by covering absorbed
impurity such as carbon owing to impurity gas absorbed in the first
protective film 151.
[0204] Concretely, during the manufacturing processes, the emission
amount of gas containing unnecessary component incident to the
exhaustion processes is reduced to about 1/5 of the amount
resulting when adopting the conventional method. This indicates
that during the processes performed in the atmospheric air, the
protective layer is dramatically prevented from absorbing gas
containing unnecessary component. As a result, a time required for
exhaustion during panel sealing is reduced to about 1/2.
[0205] In addition, by forming the second protective film on an
entire surface of the first protective film, it becomes possible to
lower the manufacturing cost by reducing the time required for
exhaustion during the sealing exhaustion process in PDP
manufacturing. At the same time, it is possible to lower the
driving voltage according to the manufacturing method of PDP.
Consequently, the resulting PDP is expected to have a lowered
driving circuit cost by lowering the driving voltage.
[0206] Note that in the above description, impurity to be
incorporated in the first protective film is explained to be H.
However alternatively, the impurity may be Cl, F, which can form a
dangling bond, or a combination therebetween. The film is formable
by mixing these gasses into Ar gas.
[0207] In addition, the film thickness of the first protective film
is explained to be about 600 nm, and the film thickness of the
second protective film is explained to be about 30 nm. However, the
film thicknesses of the first and second protective films are
respectively adjusted as long as they fall within the range of 10
nm-1 .mu.m. Preferably, however, the second protective film should
be thin with respect to the first protective film so that the
second protective film can be removed by sputtering as a result of
discharge in the initial stage of the discharge after the PDP
completes after sealing. The second protective film is preferably
in the range of 10 nm to 100 nm. If the second protective film is
thin such as about 10 nm, the film can be formed evenly on a
predetermined are a. However the film thickness falls outside this
range, the resulting film sometimes becomes scattered in
island-like formation.
Third and Forth Embodiments
[0208] FIGS. 10A and 10B are respectively a sectional diagram and a
plan conceptual diagram showing a schematic structure of a
discharge cell around the front panel, regarding the third
embodiment.
[0209] As shown in these drawings, a second protective film 153 of
a protective layer 15 is formed in stripe formation on a surface of
a first protective film 151, where BaO is used as a base material
of both of the first protective film 151 and the second protective
film 153. The are a ratio of an overlapping part of the second
protective film 153 with the display electrodes 12, 13 is about 30%
with respect to the width W of each one display electrode 12, 13.
FIGS. 11A and 11B are respectively a sectional diagram and a plan
conceptual diagram showing a schematic structure of a discharge
cell around the front panel. In the fourth embodiment, a first
protective film 151 made of BaO is formed on a surface of the
dielectric layer 14, and a second protective film 154 is formed
thereon so that the first protective film 151 is exposed in
fence-like formation. The are a ratio of an overlapping part of the
second protective film 154 with the display electrodes 12, 13 is
about 80% with respect to the width W of each one display electrode
12, 13.
[0210] The film thickness of the first protective film is set in
the range of 10 nm-1 .mu.m. The film thickness of the first
protective film is for example set as about 600 nm. On the other
hand, the film thickness of the second protective film is set as in
the range of 10 nm to 100 nm inclusive, which is thinner than the
film thickness of the first protective film.
[0211] Here, in the first protective film 151, Si is doped as
impurity with a concentration range of
1.times.10.sup.18-23/cm.sup.3. The material for doping is not
limited to Si, and may be at least one of H, Cl, F, Ge, and Cr.
[0212] Note that the first protective film and the second
protective film are both formable using a metal oxide material that
contains at least one of MgO, CaO, BaO, SrO, MgNO, and ZnO, as a
base material.
[0213] When the third and fourth embodiments having the stated
structures are driven, the electrons in the second protective films
153 and 154 of a high purity are excited and activated up to the
vicinity of the conductive zone, thereby realizing high secondary
electron emission efficiency. In addition, the first protective
film 151 in which Si and the like is doped helps reduce the
incorporation of unnecessary gas component into the protection
layer, and so it becomes possible to reduce the amount of the gas
component to be emitted in the discharge space. As a result, the
protective layer 15 as a whole is endowed with high
functionality.
[0214] Here, the tests conducted using the embodiment examples
having the structure of the third embodiment have proved that the
third embodiment has substantially the same effect as those of the
first and second embodiments. Furthermore, it is proved that the
protective layer 15 of the third embodiment has further improved
secondary electron emission factor .gamma., which is about 0.32. As
a result, the discharge starting voltage is largely reduced to the
level of about 115V in comparison to the conventional value of
180V, confirming the enlargement of driving margin.
[0215] In addition, the measurement test conducted using the
embodiment examples of the fourth embodiment has also confirmed the
excellent effects being substantially the same as those of the
embodiment examples of the third embodiment.
[0216] (Manufacturing Method) [0217] (a) After forming the
dielectric layer 14, a BaO film is formed in a sputtering apparatus
under a condition where the atmospheric air is blocked. By forming
a BaO film by blocking the air in this way, unnecessary gas such as
CO.sub.2 and H.sub.2O is prevented from entering the BaO film.
[0218] Here, a high purity MgO target is sputtered within the Ar
gas in the sputtering apparatus via a metal mask (not shown in the
drawing), thereby forming a genuine BaO film.
[0219] In addition, Ar ions in plasma state are sputtered onto the
BaO target in which Si is mixed. As a result, a first protective
film 151 having a film thickness of about 600 nm is formed on a
surface of the dielectric layer 14.
[0220] Here, the Si impurity content is desirably in the range of
1.times.10.sup.18-23/cm.sup.3. If the dope amount of the impurity
is too small, the secondary electron emission efficiency becomes
the same level as in the conventional cases. If the dope amount
becomes too large, the film resistance becomes too low, thereby
making it difficult to retain wall charge that corresponds to
written data. According to this adjustment, the first protective
film 151, which is made of a BaO film more activated than
conventionally, can further improve the second electron emission
efficiency than MgO, although becoming apt to absorb unnecessary
impurity gas such as carbon generated during the manufacturing
processes. [0221] (b) Next, on the surface of the first protective
film 151, second protective films 153 and 154 are formed in a
predetermined pattern. This is for example performed by sputtering
the high purity MgO target within the Ar gas in the sputtering
apparatus via a metal mask (not shown in the drawing) for which a
predetermined patterning has been provided.
[0222] Then the second protective films 153 and 154 of the genuine
MgO film are formed with a film thickness of about 50 nm. Here, the
second protective films 153 and 154 are formed so that a ratio of
their respective are a under a corresponding display electrode 12
is a predetermined value with respect to a width W of the display
electrode 12.
[0223] Note that the second protective film 154 may also be formed
in irregular pattern such that its portions scatter in island-like
formation, with a thickness in the range of 10 nm to 30 nm
inclusive.
[0224] In addition, if the second protective film is formed on the
first protective film so that at least part of the first protective
film under a corresponding display electrode be exposed, a time
required for exhaustion is reduced in the sealing exhaustion
process in the PDP manufacturing, thereby reducing manufacturing
cost. In addition, this arrangement is able to lower the driving
voltage thereby enabling a manufacturing method of PDP by which a
driving circuit cost is reduced.
[0225] In addition, in the above explanation, the protective layer
is formed using a sputtering method. However alternatively, an
electron beam evaporation method, a CVD method, a combination of
the methods may be used too. However, it is at least desirable to
form the first protective film using the sputtering method, for the
purpose of further improving the second electron emission
efficiency and the sputtering resistant characteristics of the
resulting protective layer.
INDUSTRIAL APPLICABILITY
[0226] A gas discharge panel according to the present invention is
applicable to a large-size television, a high-definition
television, or a large-size display apparatus. Accordingly, the gas
discharge panel according to the present invention is applicable in
a film-related apparatus industry, an advertisement apparatus
industry, and industries dealing with industrial apparatuses and
other apparatuses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0227] FIG. 1 is a sectional perspective diagram showing a
structure of a PDP according to the first embodiment.
[0228] FIG. 2 is a diagram showing an example of driving processes
of the PDP.
[0229] FIG. 3 is a graph showing a relation between compositions of
a protective layer and discharge variability.
[0230] FIG. 4 is a graph showing a detailed relation between
compositions of a protective layer and discharge variability.
[0231] FIG. 5 is a graph showing a relation between compositions of
a protective layer, discharge delay, and wall charge retaining
power index.
[0232] FIG. 6 is a graph showing a relation between a light
emission wavelength and light emission intensity in
cathodoluminescence spectroscopy.
[0233] FIG. 7 is a graph showing a relation between discharge
variability and light emission intensity in cathode
luminescence.
[0234] FIG. 8 is a graph showing a relation between discharge
starting voltage and light emission intensity in
cathodoluminescence spectroscopy.
[0235] FIG. 9 is a sectional conceptual diagram showing a structure
around a protective layer of a PDP according to the second
embodiment.
[0236] FIG. 10A is a sectional conceptual diagram showing a
structure of a discharge cell around a front panel according to the
second embodiment, and FIG. 10B is a plan conceptual diagram of
FIG. 10A.
[0237] FIG. 1A is a sectional conceptual diagram showing a
structure regarding a front panel in another embodiment example
according to the second embodiment, and FIG. 11B is a plan
conceptual diagram of FIG. 11A.
[0238] FIG. 12 is a diagram showing a difference of absorption
amount when leaving a protective layer to stand.
EXPLANATION OF REFERENCE SIGNS
[0239] 1 PDP [0240] 10 front panel [0241] 11 front panel glass
[0242] 12 scan electrode [0243] 13 sustain electrode [0244] 14,19
dielectric layer [0245] 15 protective layer [0246] 16 back panel
[0247] 17 back panel glass [0248] 18 address electrode [0249] 20
barrier rib [0250] 23 phosphor layer [0251] 31,32 discharge cell
[0252] 33 display electrode [0253] 34,35,36,37 protective layer
[0254] 121,131 bus electrode [0255] 151,152 first protective film
[0256] 153,154 second protective film
* * * * *